1.什么是分頁(yè)?

分頁(yè)是一種將包含多個(gè)記錄的列表拆分為子列表的技術(shù)。例如，您在Google上使用關(guān)鍵字搜索并收到數(shù)以萬(wàn)計(jì)的結(jié)果。但是，每個(gè)Google頁(yè)面只為您顯示 10 個(gè)結(jié)果。其他結(jié)果將在下一頁(yè)顯示。

在使用Hibernate的Java應(yīng)用程序中，一個(gè)查詢(xún)語(yǔ)句可以返回一個(gè)記錄列表，并且您會(huì)問(wèn)這樣一個(gè)問(wèn)題，即如何只獲取列表的一部分(從位置N1 到位置N2的記錄)，并獲取有關(guān)總記錄的信息和總頁(yè)數(shù)。

休眠與 JPA

Hibernate和JPA是兩種相同的技術(shù)。如果您了解 Hibernate， 則可以輕松地使用JPA，反之亦然。但是，它們也有一些區(qū)別。其中一個(gè)區(qū)別是Hibernate提供了比JPA更好的分頁(yè)技術(shù)。在本課中，我將指導(dǎo)您使用Hibernate 5的分頁(yè)技術(shù)。請(qǐng)注意，該技術(shù)不受JPA支持。

2.使用 Hibernate 進(jìn)行分頁(yè)

您需要做的就是創(chuàng)建一個(gè)Query對(duì)象，并提供page、maxResult、maxNavigationResult 參數(shù)來(lái)創(chuàng)建一個(gè)PaginationResult對(duì)象。PaginationResult

是一個(gè)實(shí)用程序類(lèi)，可幫助您實(shí)現(xiàn)查詢(xún)并返回適合上述參數(shù)的記錄列表。

package org.o7planning.tutorial.hibernate.pagination;
import java.util.ArrayList;
import java.util.List;
import org.hibernate.ScrollMode;
import org.hibernate.ScrollableResults;
import org.hibernate.query.Query;
public class PaginationResult<E> {
    private int totalRecords;
    private int currentPage;
    private List<E> list;
    private int maxResult;
    private int totalPages;
    private int maxNavigationPage;
    private List<Integer> navigationPages;
    // @page: 1, 2, ..
    public PaginationResult(Query<E> query, int page, int maxResult, int maxNavigationPage) {
        final int pageIndex = page - 1 < 0 ? 0 : page - 1;
        int fromRecordIndex = pageIndex * maxResult;
        int maxRecordIndex = fromRecordIndex + maxResult;
        ScrollableResults resultScroll = query.scroll(ScrollMode.SCROLL_INSENSITIVE  );
        List<E> results = new ArrayList<E>();
        boolean hasResult =   resultScroll.first();
        if (hasResult) {        
            // Scroll to position:
             hasResult = resultScroll.scroll(fromRecordIndex);
            if (hasResult) {
                do {
                    E record = (E) resultScroll.get(0);
                    results.add(record);
                } while (resultScroll.next()//
                        && resultScroll.getRowNumber() >= fromRecordIndex
                        && resultScroll.getRowNumber() < maxRecordIndex);
            }
            // Go to Last record.
             resultScroll.last();
        } 
        // Total Records
        this.totalRecords = resultScroll.getRowNumber() + 1;
        this.currentPage = pageIndex + 1;
        this.list = results;
        this.maxResult = maxResult;
        if (this.totalRecords % this.maxResult == 0) {
            this.totalPages = this.totalRecords / this.maxResult;
        } else {
            this.totalPages = (this.totalRecords / this.maxResult) + 1;
        }
        this.maxNavigationPage = maxNavigationPage;
        if (maxNavigationPage < totalPages) {
            this.maxNavigationPage = maxNavigationPage;
        }
        resultScroll.close();
        this.calcNavigationPages();
    }
    private void calcNavigationPages() {
        this.navigationPages = new ArrayList<Integer>();
        int current = this.currentPage > this.totalPages ? this.totalPages : this.currentPage;
        int begin = current - this.maxNavigationPage / 2;
        int end = current + this.maxNavigationPage / 2; 
        // The first page
        navigationPages.add(1);
        if (begin > 2) {    
            // Using for '...'
            navigationPages.add(-1);
        }
        for (int i = begin; i < end; i++) {
            if (i > 1 && i < this.totalPages) {
                navigationPages.add(i);
            }
        }
        if (end < this.totalPages - 2) { 
            // Using for '...'
            navigationPages.add(-1);
        }    
        // The last page.
        navigationPages.add(this.totalPages);
    }
    public int getTotalPages() {
        return totalPages;
    }
    public int getTotalRecords() {
        return totalRecords;
    }
    public int getCurrentPage() {
        return currentPage;
    }
    public List<E> getList() {
        return list;
    }
    public int getMaxResult() {
        return maxResult;
    }
    public List<Integer> getNavigationPages() {
        return navigationPages;
    }
}

例子：

package org.o7planning.tutorial.hibernate.entities; 
import java.util.Date;
import java.util.HashSet;
import java.util.Set; 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;
@Entity
@Table(name = "EMPLOYEE", //
        uniqueConstraints = { @UniqueConstraint(columnNames = { "EMP_NO" }) })
public class Employee {
    @Id
    @Column(name = "EMP_ID")
    private Long empId; 
    @Column(name = "EMP_NO", length = 20, nullable = false)
    private String empNo; 
    @Column(name = "EMP_NAME", length = 50, nullable = false)
    private String empName; 
    @Column(name = "JOB", length = 30, nullable = false)
    private String job; 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "MNG_ID")
    private Employee manager; 
    @Column(name = "HIRE_DATE", nullable = false)
    @Temporal(TemporalType.DATE)
    private Date hideDate; 
    @Column(name = "SALARY", nullable = false)
    private Float salary; 
    @Lob
    @Column(name = "IMAGE", length = Integer.MAX_VALUE, nullable = true)
    private byte[] image; 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "DEPT_ID", nullable = false)
    private Department department; 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "empId")
    private Set<Employee> employees = new HashSet<Employee>(0); 
    // Getter & Setter 
}

package org.o7planning.tutorial.hibernate.entities; 
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint; 
@Entity
@Table(name = "DEPARTMENT", //
        uniqueConstraints = { @UniqueConstraint(columnNames = { "DEPT_NO" }) })
public class Department {
    @Id
    @Column(name = "DEPT_ID")
    private Integer deptId; 
    @Column(name = "DEPT_NO", length = 20, nullable = false)
    private String deptNo;
    @Column(name = "DEPT_NAME", nullable = false)
    private String deptName; 
    @Column(name = "LOCATION")
    private String location; 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "department")
    private Set<Employee> employees = new HashSet<Employee>(0); 
    public Department() {
    }   
    // Getter & Setter
}

package org.o7planning.tutorial.hibernate.beans;
public class EmployeeInfo {
    private Long empId;
    private String empNo;
    private String empName;
    private String deptNo;
    private String deptName;
    public EmployeeInfo() {
    }
    // This constructor is used by Hibernate Query.
    public EmployeeInfo(Long empId, String empNo, String empName, String deptNo, String deptName) {
        this.empId = empId;
        this.empNo = empNo;
        this.empName = empName;
        this.deptNo = deptNo;
        this.deptName = deptName;
    }
    // Getter & Setter
}

例子：

package org.o7planning.tutorial.hibernate.pagination;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;
public class PaginationExample1 {
    public static void main(String[] args) {
        // Have sessionFactory object...
        SessionFactory factory = HibernateUtils.getSessionFactory();
        Session session = factory.getCurrentSession();
        String sql = "Select e from " + Employee.class.getName() + " e " //
                + " Where e.empId > :empId ";
        Query<Employee> query = session.createQuery(sql, Employee.class);
        query.setParameter("empId", 100);
        int page = 1;
        int maxResult = 20;
        int maxNavigationResult = 10;
        PaginationResult<Employee> result = new PaginationResult<Employee>(query, page, maxResult, maxNavigationResult);
        // Result:
        List<Employee> emps = result.getList();
        int totalPages = result.getTotalRecords();
        int totalRecords = result.getTotalRecords();
        // 1 2 3 4 5 ... 11 12 13
        List<Integer> navPages = result.getNavigationPages();
    }
}

例子：

package org.o7planning.tutorial.hibernate.pagination;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.beans.EmployeeInfo;
import org.o7planning.tutorial.hibernate.entities.Employee;
public class PaginationExample2 {
    public static void main(String[] args) {
        // Get sessionFactory object...
        SessionFactory factory = HibernateUtils.getSessionFactory();
        Session session = factory.getCurrentSession();
        String sql = "Select new " + EmployeeInfo.class.getName() //
                + " (e.empId,e.empNo,e.empName,d.deptNo,d.deptName) " //
                + " from " + Employee.class.getName() + " e " //
                + " Join e.department d " //
                + " Order by e.empNo ";
        Query<EmployeeInfo> query = session.createQuery(sql, EmployeeInfo.class);
        int page = 1;
        int maxResult = 20;
        int maxNavigationResult = 10;
        PaginationResult<EmployeeInfo> result
             = new PaginationResult<EmployeeInfo>(query, page, maxResult, maxNavigationResult);
        // Result:
        List<EmployeeInfo> emps = result.getList();
        int totalPages = result.getTotalRecords();
        int totalRecords = result.getTotalRecords();
        // 1 2 3 4 5 ... 11 12 13
        List<Integer> navPages = result.getNavigationPages();
    }
}

以及使用PaginationResult的JSP代碼片段的示例 ：

<c:if test="${paginationProducts.totalPages > 1}">
   <div class="page-navigator">
      <c:forEach items="${paginationProducts.navigationPages}" var = "page">
         <c:if test="${page != -1 }">
            <a href="productList?page=${page}" class="nav-item">${page}</a>
         </c:if>
         <c:if test="${page == -1 }">
            <span class="nav-item"> ... </span>
         </c:if>
      </c:forEach>
   </div>
</c:if>

通過(guò)上述介紹，相信大家對(duì)Hibernate分頁(yè)是什么已經(jīng)有所了解，大家如果想了解更多相關(guān)知識(shí)，可以關(guān)注一下動(dòng)力節(jié)點(diǎn)的Java視頻，里面的課程內(nèi)容詳細(xì)，通俗易懂，適合沒(méi)有基礎(chǔ)的小伙伴學(xué)習(xí)，希望對(duì)大家能夠有所幫助。